Epidemiological studies have suggested gender differences in the development of hypertrophy and heart disease, but the mechanism and the role of estrogen receptor subtypes is not established. The goal of this study was to determine the role of estrogen receptor subtypes in the development of pressure overload hypertrophy in mice. We performed transverse aortic constriction (TAC) and sham operations in male and female wild type (WT) mice and mice lacking functional alpha estrogen receptor (alpha-ERKO) and mice lacking beta estrogen receptor (beta-ERKO). Body, heart, and lung weights were measured 2 weeks post surgery. WT male mice subjected to TAC showed a 64% increase in heart to body weight (HW/BW) ratio compared to sham, and WT males have increased lung weight at 2 weeks. WT female mice subjected to TAC showed a 31% increase in HW/BW compared to sham, which was significantly less than their male counterparts and no evidence of heart failure. Alpha-ERKO females developed a HW/BW ratio nearly identical to that seen in WT littermate females in response to TAC, indicating that the alpha estrogen receptor is not essential for the attenuation of hypertrophy observed in WT females. In contrast, beta-ERKO females responded to TAC with a significantly greater increase in HW/BW ratio than WT littermate females. Beta-ERKO females have lower expression of lipoprotein lipase at baseline than WT or alpha-ERKO females. These data suggest an important role for the beta-estrogen receptor in attenuating the hypertrophic response to pressure overload in females. Although estrogen has effects on the heart, little is know regarding which genes in the heart are directly responsive to estrogen. We identified a potential ERE enhancer sequence located in the first intron of the mouse lipoprotein lipase (LPL) gene. The potential EREs were linked to TATA-LUC reporter plasmid. The Qiagen Effectene transfection method was used to detect mouse LPL estrogen response elements linked to TATA LUC reporter activity. A transient transfection assay shows that both ER-alpha and ER-beta have strong activity on the heterologous promoter reporter in Hela cells upon addition of estrogen. Both ER-a activity and ER-beta activity on the LPL EREs were abrogated by estrogen antagonist ICI. To test whether LPL expression in heart is regulated by estrogen we perfused mouse hearts from ovariectomized females (OVX) with 100nM estradiol or vehicle for 2 hours after which hearts were frozen and RNA was isolated. The SYBR green real-time PCR method was used to detect LPL gene expression normalized to GAPDH. Consistent with estrogen regulation of LPL we found addition of estradiol to hearts from OVX females resulted in a significant increase in LPL expression (247.7% increase vs. vehicle treated). These results show that heart LPL is a potential estrogen responsive gene. We also examined male-female difference in an ischemia-reperfusion model of injury. Under hypercontractile conditions associated with increased intracellular calcium, male hearts show enhanced ischemia/reperfusion injury compared to female hearts. Our aim in this study was to identify the specific estrogen receptor involved, and the mechanism responsible for this gender difference. Following brief treatment with isoproterenol,a B-adrenergic receptor agonist, isolated mouse hearts were subjected to ischemia and reperfusion. Postischemic contractile function and infarct size were measured in wild-type (WT) male and female hearts, and female hearts lacking functional alpha estrogen receptor (alpha-ERKO), or the beta estrogen receptor (beta-ERKO). WT males exhibited significantly less functional recovery and more necrosis than WT females. Alpha-ERKO females exhibited ischemia-reperfusion injury similar to that observed in WT females, whereas ??ERKO females exhibited significantly less functional recovery and more necrosis than WT females and were more similar to WT males. These data suggest that estrogen, through the beta-estrogen receptor, plays a role in the protection observed in the female heart. Furthermore, we performed DNA microarray analysis to identify genes that were differentially expressed in beta-ERKO female hearts compared to alpha-ERKO and WT female hearts, and found altered expression of a number of metabolism genes in beta-ERKO females compared to alpha-ERKO and WT females, which may be important in ischemic injury. We also investigate whether treatment with a selective ER-beta agonist (2,3-bis(4-hydroxyphenyl)-propionitrile, DPN) can provide cardioprotection. Using increase in uterine weight as a measure of alpha-ER activation, we first determine that estradiol, but not DPN resulted in an increased uterine weight. Ovariectomized (ovx) female mice were treated with estradiol, a selective ER-beta agonist, or vehicle for two weeks using subcutaneously implanted Alzet mini-osmotic pumps. Isolated Langendorff-perfused hearts were perfused for 25 minutes prior to a one minute treatment with isoproterenol, followed by 20 minutes of normothermic global ischemia and 40 minutes of reperfusion. Left ventricular developed pressure (LVDP) and heart rate were measured using a latex balloon inserted into the left ventricle and connected to a pressure transducer. Recovery of cardiac function at the end of the 40 minutes of reperfusion was expressed as the percentage of the pre-ischemic rate pressure product (RPP = LVDP x heart rate). We observed that the hearts from ovariectomized female mice had a significantly lower functional recovery than the hearts from intact female mice. Furthermore, hearts from ovariectomized female mice treated with a selective YaER agonist exhibited significantly better functional recovery than hearts from either vehicle treated ovariectomized female mice or wild type male mice. These findings suggest that under hypercontractile conditions, a selective ER-beta agonist has a cardioprotective effect in the mouse ischemia-reperfusion injury model.